Sampling Methods

Sampling methods used for this study are detailed in Tagliaferri and others (2021). Sediment and groundwater samples were collected between June 2018 and June 2019 at selected sites along the northern shore of Great South Bay. All water-quality and sediment data collected in the field and those analyzed in laboratories as part of this study are available from the U.S. Geological Survey (USGS) National Water Information System (NWIS) database (U.S. Geological Survey, 2020a).

Wet conditions were defined as more than 0.25 inch of precipitation in 24 hours or 0.50 inch in 48 hours. Dry conditions were defined as less than 0.25 inch of precipitation in 72 hours. Rainfall totaled 0.20 inch on July 25, 2018, and 0.07 inch on July 26, 2018, designating samples collected on July 26, 2018, in Great South Bay as summer wet samples (more than 0.25 inch within 24 hours). Wet winter samples were collected in Great South Bay on April 16, 2019, with 0.75 inch of precipitation falling on April 15, 2019. Rainfall values were obtained from Islip Long Island MacArthur Airport (National Oceanic and Atmospheric Administration, 2021).

From June 2018 to June 2019, 8 surface-water sites were sampled in and around Great South Bay, yielding 32 surface-water samples, 2 groundwater samples, and 2 sediment samples. Of the surface-water sites, four were considered to be source sites (waters flowing directly into Great South Bay from the land), and four were considered to be receptor sites (the bay itself). Sixteen surface-water samples were collected under wet conditions, and 16, under dry conditions; 16 surface-water samples were collected in the summer, and 16, in the winter.

Laboratory Methods

Laboratory methods used for this study are detailed in Fisher and others (2020) and Tagliaferri and others (2021). Samples for fecal coliforms were analyzed at the Suffolk County Department of Health Services Public Environmental Health Laboratory (PEHL) and the NYSDEC Marine Laboratory. Additional information was either observed or compiled to facilitate interpretation of data. Precipitation measurements from the MacArthur Airport weather gage, which is approximately 7 miles from the center of Great South Bay (National Oceanic and Atmospheric Administration, 2021), were used to determine wet or dry conditions. Quality assurance for samples collected at MacArthur Airport weather gage is available in Menne and others (2012). Relative tide stage as noted by USGS field personnel and verified based on tidal predictions available (National Oceanic and Atmospheric Administration, undated) was documented along with the sample information in NWIS (U.S. Geological Survey, 2020a). Land-cover and sewer district geographic information system (GIS) coverages (Nassau County, 2015; Suffolk County, 2020; U.S. Geological Survey, 2020b) were used for data interpretation. These data support the MST results to increase confidence in the geographical source of the water and likely transport mechanisms of fecal contamination to Great South Bay.

Microbial Source Tracking

The canine Bacteroides (BacCan) marker was the most frequently detected MST marker with 15 positive detections in surface water across the landscape, followed by the waterfowl Helicobacter (GFD) marker with 9 detections and the human Bacteroides (HF183) marker with 4 detections in surface water (excluding 2 detections in sediment). The ruminant Bacteroides (Rum2Bac) marker was not detected in any samples collected during this study. The detection frequency of BacCan was similar for all sampling conditions and seasons (table 1), suggesting canine influence is unrelated to weather events and is a year-round occurrence. BacCan was detected in 14 of 16 source samples and only 1 of 16 receptor samples, which suggests that canine fecal contamination is likely diluted in the bay. There was a similar amount of marker detections when comparing sampling condition (wet or dry) and season (winter or summer), suggesting that fecal contamination was unrelated to weather events or time of year. Eight waterfowl marker detections were in samples collected during the winter, and only one during the summer, implicating seasonal avian fecal contamination throughout the embayment. The human marker was detected in only one surface-water receptor sample, during the wet winter sampling event at the Green Creek Mid-Bay site. Three of four human marker detections were in the samples collected during the wet winter sampling event, indicating that weather and season may influence the presence of human markers in Great South Bay, but human markers are not overly prevalent as a whole.

Host Specific Markers

Reporting limits for the three predominant MST markers (HF183, BacCan, and GFD) detected in Great South Bay varied slightly because of analytical processes, such as dilutions required because of matrix interferences. Understanding occurrence of the predominant MST markers in Great South Bay can help prioritize locations for additional investigation and infrastructure improvement. It can also provide a baseline for host contributions when prioritizing sites of concern for assessing FC and after total maximum daily load implementation.

HF183

The human marker was detected in 4 of 32 total surface water samples, all of which were in samples associated with Green Creek. Three of four samples with positive HF183 detections (450, 500, and 1,000 copies per 100 milliliters [copies/100 mL]) were in wet winter conditions, and the remaining sample (1,470 copies/100 mL) was collected during dry summer conditions (fig. 3). The Green Creek Mid-Bay site was the only surface-water receptor site with a positive HF183 detection. The highest concentration of HF183 was observed in a sample collected at the Green Creek County Park site (1,470 copies/100 mL) and was associated with relatively high FC concentration (1,300 most probable number per 100 milliliters [MPN/100 mL]; table 1.2). Sediment samples collected at the Foster Avenue Beach and Beach at Long Island Maritime Museum sites had positive detections of HF183 (200 and 670 copies per gram dry weight [copies/gdw], respectively), but the associated groundwater samples at both sites were negative for HF183 detection. HF183 in the sediment likely does not originate from groundwater in these areas but rather from tidal overwash.

BacCan

The canine marker was detected in 15 of 32 surface water samples and was found in samples associated with both Brown and Green Creeks. The concentration of BacCan in all samples was of the same order of magnitude (thousands of copies per 100 milliliters [mL]), except at the Green Creek Culvert at Montauk Highway site (121,000 copies/100 mL in the sample collected under summer wet conditions). The relatively even split of positive BacCan detections between sampling conditions (wet versus dry) and season (summer versus winter) suggests year-round canine influence across the Great South Bay landscape (table 1). The highest concentration (121,000 copies/100 mL) of BacCan in the sample collected at the Green Creek Culvert at Montauk Highway site during wet summer conditions was associated with the second highest FC concentration observed in Great South Bay during this study (1,700 MPN/100 mL; table 1.2; U.S. Geological Survey, 2020a). The Brown Creek Culvert at Middle Road and Green Creek County Park sites were the two sites where all samples collected contained positive detections of BacCan. The Brown Creek Mid-Bay site was the only receptor site with a sample positive for BacCan, which was in dry summer conditions (fig. 4). There were no positive detections of BacCan in the sediment or groundwater samples collected at the Foster Avenue Beach or Beach at Long Island Maritime Museum sites.

GFD

The waterfowl marker was detected in 9 of 32 total samples and was in samples associated with both Brown and Green Creeks. All positive detections were between hundreds and thousands of copies per 100 mL. The Green Creek County Park site was the only site with no GFD detections (fig. 5). Positive GFD detections were split roughly between weather condition (wet or dry) and sample type (source or receptor; table 1). Eight of nine positive detections were in samples collected during the winter season, implicating seasonal avian fecal contamination throughout the embayment (fig. 5). The waterfowl marker was present in each receptor sample collected in dry, winter conditions, whereas detections in source samples primarily occurred in wet conditions. The highest concentrations of GFD were in samples collected at two different receptor sites and both during dry winter conditions, at the Green Creek Mid-Bay (3,300 copies/100 mL) and Green Creek Mouth (2,500 copies/100 mL) sites. The highest frequencies of positive GFD detections were in samples collected at the Green Creek near Montauk Highway and Mill Pond Culvert near South Street sites, each with positive detections in two of four samples. There were no positive detections of GFD in the groundwater samples collected at the Foster Avenue Beach or Beach at Long Island Maritime Museum sites.

Fecal Coliform Bacteria

All 16 receptor samples had concentrations that were below the NSSP-defined 49 MPN/100 mL threshold for shellfish bed closure, despite the area surrounding Brown and Green Creeks being uncertified under the NSSP year-round (U.S. Food and Drug Administration, 2019). The highest FC concentrations in receptor sites were at the Brown Creek Mouth (45 MPN/100 mL) and Green Creek Mouth (43 MPN/100 mL) sites under wet sampling conditions. In contrast, 11 of 16 source samples had concentrations that exceeded 49 MPN/100 mL, indicating a high potential for inland contamination to affect the bay. The highest FC concentration observed in all Great South Bay samples was 5,000 MPN/100 mL, collected at the Brown Creek Culvert near Middle Road site in wet, summer conditions. The highest FC concentrations for each source site were during the summer season and were associated with high concentrations of canine markers.

The relation between FC and marker detection is not straightforward. Fecal coliform and specific host-associated markers may decay at different rates and be present in different abundances. Host-associated markers were shown to decay more rapidly than FC in Drozd and others (2011) and Rogers and others (2011). In general, high FC concentrations were in samples collected during the summer season and in wet weather.

Nonpoint Sources of Fecal Coliform Bacteria

A potential, major nonpoint contributor of FC to Great South Bay includes groundwater seepage from the widespread use of onsite wastewater disposal systems, which have the potential for leakage and failure, which in turn would contaminate the groundwater. Fecal coliform concentrations for groundwater collected at the Beach at Long Island Maritime Museum site were below detection and fecal coliform was not analyzed for the Foster Beach Avenue site. There were no MST markers associated with these groundwater samples.

Recent research (O’Mullan and others, 2019; Hassard and others, 2016) indicated that resuspension of sediment along natural shorelines can cause a spike in fecal indicator bacteria in the water column. Therefore, it is possible that during conditions that result in high wave energy, sediment (particularly organic-rich material) can act as a source of FC when resuspended in the water column as a result of tidal movement, storms, or boat activity. Human markers were detected in the sediment at the Beach at Long Island Maritime Museum (670 copies/gdw) and Foster Avenue Beach (200 copies/gdw) sites. Data from sediment samples collected throughout Long Island for the area-wide MST study strongly suggest that sandy sediment is an unlikely contributor of FC in all embayments, including Great South Bay.

Green Creek Culvert at Montauk Highway—Class 1

The highest instances of FC concentrations at the Green Creek Culvert at Montauk Highway site were in the summer samples, with 1,700 MPN/100 mL detected in the wet summer sample, and 800 MPN/100 mL, in the dry summer sample. Waterfowl and canine markers were most frequently detected in addition to one human detection, which was in the wet winter sample. The one human marker detection at this site was at a relatively low concentration (450 copies/100 mL) and corresponded with an FC concentration of 110 MPN/100 mL. The highest FC concentration at this site (1,700 MPN/100 mL) corresponded to the highest canine marker detection (121,000 copies/100 mL) in Great South Bay. Fecal coliform concentrations in the dry winter sample were right at the detection limit (20 MPN/100 mL) and were negative for all markers. Fecal coliform concentrations were higher in the summer (1,700 and 800 MPN/100 mL) than in the winter (20 and 110 MPN/100 mL), which may be explained by an increase in human, canine, and waterfowl populations in the summer season. The higher FC concentrations in summer and winter wet samples compared with their respective dry samples suggest an influence from stormwater conveyances and runoff from impervious surfaces.

Green Creek County Park—Class 1

All fecal coliform concentrations at the Green Creek County Park site were at or above the 20-MPN/100 mL reporting limit, ranging from 20 to 1,300 MPN/100 mL. Canine markers were detected in all samples, with the second highest concentration in Great South Bay in the wet winter sample from this site (13,000 copies/100 mL). Of all Great South Bay samples, human marker concentrations at this site were the highest, with concentrations that exceeded 1,000 copies/100 mL, and were associated with high FC concentrations during wet and dry weather. Private boat docks along the bank of Green Creek and a marina (just upstream from Green Creek County Park) are a potential source of these human marker detections, particularly in dry weather during the summer boating season; however, the human marker detected in the wet winter samples was also detected upstream at the Green Creek Culvert at Montauk Highway site and may be related to failing septic systems along the densely populated shoreline. More targeted sampling is needed in this area to determine human waste contributions to FC loads. The wet and dry summer samples at the Green Creek County Park site exhibited FC concentrations of more than 1,100 and 1,300 MPN/100 mL, respectively, whereas the samples taken upstream at the Green Creek Culvert at Montauk Highway site contained 1,700 and 800 MPN/100 mL respectively, suggesting high FC concentrations throughout the length of Green Creek in all weather conditions during the summer. These data demonstrate that Green Creek is a source of FC to Great South Bay, particularly during the summer, primarily attributed to the increased presence of canine markers in the surrounding area.

Brown Creek Culvert at Middle Road—Class 2

The sample collected at the Brown Creek Culvert at Middle Road site during wet summer conditions had the highest fecal coliform concentration (5,000 MPN/100mL) in all Great South Bay. Canine markers were detected in all samples, but these detections were not always associated with high FC. For example, the dry winter sample contained canine markers but had concentrations below detection for FC, whereas the summer samples contained both high FC and canine marker concentrations. No human or ruminant markers were detected at this site. Fecal coliform concentrations were higher in samples collected under wet conditions than dry, which implies that stormwater was flushing canine waste from the open grassy areas and surrounding residential communities into Brown Creek. Higher fecal coliform concentrations in the summer than the winter may reflect heavier use of the surrounding area for dog walking.

Mill Pond Culvert near South Street—Class 2

Fecal coliform concentrations at the Mill Pond Culvert near South Street site ranged from below the detection level in the wet winter sample to 300 MPN/100 mL in the wet summer sample. Canine markers were detected in three of four samples at concentrations ranging from 3,000 copies/100 mL in the wet winter sample to 5,800 copies/100 mL in the dry winter sample. Waterfowl markers were only detected in the winter samples and were associated with low to no detections of FC. Wet summer samples generally had higher FC concentrations than dry summer samples, suggesting that stormwater runoff is an important contributor of FC at the Mill Pond Culvert site and to Brown Creek.

Sediment—Class 5

Fecal coliform concentrations are not available for sediment samples collected at the Foster Avenue Beach or Beach at Long Island Maritime Museum sites; however, these samples appeared to be low in organic matter and therefore less likely to retain bacteria (Lee and others, 2006). Low levels of human markers were detected in these samples (200 copies/100 mL at the Foster Avenue Beach and 670 copies/100 mL at the Beach at Long Island Maritime Museum site), indicating minimal human fecal contamination potential to Great South Bay through the sediment. Additional sediment sampling is needed to determine the full potential of human fecal contamination from beach sediments to Great South Bay.

Groundwater—Class 5

The lack of positive detections for FC in groundwater throughout the study suggests that direct groundwater seepage is an unlikely contributor of FC to Great South Bay. Human MST markers were not detected at the Foster Avenue Beach or Beach at Long Island Maritime Museum site during this study, suggesting that septic waste is not a contributor of FC to the bay.